A large number of SMTP implementations support SMTP pipelining, including:
(1) Innosoft's PMDF and Sun's SIMS.
(2) ISODE/MessagingDirect's PP.
(3) ISOCOR's nPlex.
(4) software.com's post.office.
(5) Zmailer.
(6) Smail.
(7) The SMTP server in Windows 2000.
SMTP pipelining has been widely deployed in these and other implementations for some
time, and there have been no reported interoperability problems.